A book is offered for free download as a .pdf, and do it’s sales collapse? NO! They increase.
As Stephan Kinsella notes at againstmonopoly.org
Jeff Tucker makes a similar observation on the Mises blog:
You will note that Kinsella’s book Against Intellectual Property is the #2 bestseller in the store. This is despite its having been online for six years and remains so, in two formats. What a way to demonstrate a thesis. If you have something that is valuable to others, people might be willing to pay for it